A.c. Voltage Measurements; C I R C U I T D E S C R I P T I O; G E N E R A; A D J U S T I N G T A B L - Philips PM2517E Service Manual

21
R a n g e
Attenuation
R A N G E
R N G B
R N G A
I n p u t A D C R i P f u l 2 5 1 7 E
F ET switch
v 2 0 1
10 v__
100 v-
1000 v-
1 0
1 0
'1000
1 0 0 0
0
0
1
1
0
1
0
1
0 . 1 v
0 . 1 v
10 l\,lQ
10 lvro
I tvt 0'l
9 t\,1 0'l
---o--
--r'o-
_+
_a-<-
o
T h e i n p u t c i r c u i t f o r d . c . v o l t a g e m e a s u r e m e n t s
i s s h o w n i n f i g u r e 1 2 .
ln the above mentioned table, the attenuation, the input sensitivity of the ADC and the range control are
given. The 10x attenuation is achieved with the voltage division of R 2O1 I R 2O4 and Ri of the ADC.
Adjusting the 10 x attenuator is made with resistor R 203 (coarse) and potentiometer R 204 (fine).
T h e l O O o x a t t e n u a t i o n , w h i c h i s s w i t c h e d o n b y t h e s i g n a l R N G 8 , i s a c h i e v e d b y t h e v o l t a g e d i v i s i o n o f
R 201 / R 204 with R 205 / R 208 ll Ri of the ADC.
Adjusting the IOOOX attenuator is made with the cut away resistors R 206 and R 208 (coarse) and potentio-
m e t e r R 2 0 7 ( f i n e ) .
The a.c. signals are filtered out by the combinations R2O1 , C201 and R2O2, C2O2.
3.3.2.2. A.c. voltage measurements (Fig. 13)
R a n g e
A t t e n u a i i o n
R A N G E
R N G B R N G A
I n p u t a c l d c
convertor
Ri PM 2511
E
F E T s w i t c h
v 301 v 302
I n p u t
A D C
1 0 v -
1 0 0 v -
1000 v-
'
1 0
1 0
1 0 0 0
1 0 0 0
0
0
1
1
0
l
0
I
0 . 1 v
1 V
0 . 1 v
2 l \ i l Q
2 M A
1 r\,1 802
1 r\4 801
-€o- -{o-
-{o- -/o-
--..{--....o-
q H - - } + -
1 V
' m a x . j n o u t
6 0 0 V r m s .
- T h e i n p u t c i r c u i t f o r a . c . v o l t a g e m e a s u r e m e n t s
i s s h o w n i n f i g u r e 1 3 . l n t h e a b o v e m e n t i o n e d t a b l e t h e
a t t e n u a t i o n , t h e r a n g e c o n t r o l a n d t h e i n p u t s e n s i t i v i t y o f t h e a c / d c c o n v e r t o r a n d A D C a r e g i v e n .
- T h e 1 0 x a t t e n u a t i o n i s m a d e b y t h e v o l t a g e d i v i s i o n w i t h c o m p o n e n t s R 3 0 1 ; R 3 0 2 / / C 3 0 5 ; C 3 0 6 a n d
R 3 0 6 / / C p ( p a r a s i t i c c a p a c i t a n c e s ) .
A d . c . v o l t a g e c o m p o n e n t i s b l o c k e d b y c a p a c i t o r C 3 0 1 .
- T h e 1 0 0 0 x a t t e n u a t i o n a s m a d e t h e v o l t a g e d i v i d e r R 3 0 1 ; R 3 0 2 / / C 3 0 5 ; C 3 0 6 a n d R 3 0 5 ; R 3 1 5 / /
R 3 0 6 / / C 3 0 7 a n d C p ( p a r a s i t i c c a p a c i t a n c e s ) .
T h e 1 0 0 0 x a t t e n u a t i o n i s s w i t c h e d o n b y F E T V 3 0 1 .
T h e F E T s w i t c h V 3 0 1 c a n b e c o n s i d e r e d a s a n i d e a l s w i t c h i n s e r i e s w i t h i t s o w n o n r e s i s t a n c e ( R o n ) . T h e
R o n o f F E T ' s s w i t c h V 3 0 1 g i v e s a n i n c o r r e c t m e a s u r i n g r e s u l t . T h i s i s c o m p e n s a t e d i n t h e f o l l o w i n g w a y .
T h e a t t e n u a t e d i n p u t v o l t a g e i s s u p p l i e d t o i n p u t V i n 1 a n d V i n 2 ( V i n 1 - V i n 2 ) . I n t h i s w a y t h e F E T
s w i t c h V 3 0 1 h a s n o i n f l u e n c e o n t h e 1 0 0 0 x a t t e n u a t i o n .
- AC/DC convertor.
I n t h e a c / d c c o n v e r t o r t h e d i f f e r e n c e i n v o l t a g e ( V i n 1 ' V i n 2 ) i s c o n v e r t e d i n t o a c u r r e n t . T h e c u r r e n t i s
d e t e r m r n e d
b y V i n 1 - V i n 2
. ( R = R 3 O 7 o r R 3 0 8 + R 3 1 6 ) , a n d t h e s r a t e o f s i g n a l R N G A ( s e e t a b r e , .
R
B y t h i s t h e i n p u t s e n s i t i v i t y o f t h e a c l d c c o n v e r t o r ( 0 . 1 V o r 1 V ) i s s e l e c t e d . T h e c u r r e n t i n t h e a c l d c
convertor is rectified in the current rectifier and converted into a current again by the R l\,4S section. The
c u r r e n t f r o m t h e R l \ 4 S s e c t i o n i s p r o p o r t i o n a l t o t h e R I V I S v a l u e o f t h e i n p u t s i g n a l ( V i n 1 - V i n 2 ) .
Capacitor C 302 is an integration capacitor for the RIVIS section. Capacitors C 303 and C 304 are used for
the internal automatlc zerc (AZl of the ac/dc convertor.
- Output AC/DC convertor.
The output current from the ac/dc convertor is converted into a voltage by the resistor R 310 // R 311 +
R 3 1 2 . T h e v o l t a g e i s f i l t e r e d b y R 3 1 3 a n d C 3 1 0 a n d t h e n s u p p l i e d t o t h e A D C . A d j u s t i n g t h e o u t p u t
voltage is made by adjusting resistor R 3l1 (coarse) and potenriometer R 3'12 (fine).
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